Medical information processing apparatus and medical information processing method

ABSTRACT

A medical information processing apparatus according to an embodiment includes processing circuitry. The processing circuitry calculates noise intensity from first data acquired during a first scan. The processing circuitry calculates a denoising intensity used for a denoising process based on the noise intensity and the difference between an imaging condition for the first scan and an imaging condition for a second scan, the denoising process being applied to second data obtained by the second scan.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2019-075110, filed on Apr. 10, 2019 andJapanese Patent Application No. 2020-069908, filed on Apr. 8, 2020; theentire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a medical informationprocessing apparatus and a medical information processing method.

BACKGROUND

In recent years, the method called a shrinkage method has been known asa denoising process applicable to magnetic resonance imaging (MRI). Inthis method, the denoising intensity (the amount of noise) included inan image is estimated, and a threshold for the denoising process isdetermined based on the estimated denoising intensity. In order toensure the denoising performance, the denoising intensity included inthe image needs to be estimated with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of the overall configurationof an MRI apparatus according to a first embodiment;

FIG. 2 is a flowchart illustrating the steps of a process performed bythe MRI apparatus according to the first embodiment;

FIG. 3 is a diagram illustrating a processing function of the MRIapparatus according to the first embodiment;

FIG. 4 is a diagram illustrating a processing function of the MRIapparatus according to the first embodiment; and

FIG. 5 is a diagram illustrating a processing function of the MRIapparatus according to a second embodiment.

DETAILED DESCRIPTION

An object according to an embodiment is to provide a medical informationprocessing apparatus and a medical information processing method withwhich it is possible to accurately estimate a denoising intensity.

A medical information processing apparatus provided according to anembodiment includes processing circuitry. The processing circuitrycalculates the noise intensity from first data acquired during the firstscan. The processing circuitry calculates a denoising intensity used fora denoising process based on the noise intensity and the differencebetween an imaging condition for the first scan and an imaging conditionfor the second scan, the denoising process being applied to second dataobtained by the second scan.

With reference to the accompanying drawings, a medical informationprocessing apparatus and a medical information processing methodaccording to an embodiment are described below. Embodiments are notlimited to the following embodiments. The content described in oneembodiment are also applicable to other embodiments in principle.

First Embodiment

FIG. 1 is a diagram illustrating an example of the overall configurationof an MRI apparatus 100 according to a first embodiment. For example, asillustrated in FIG. 1 , the MRI apparatus 100 according to the presentembodiment includes a static magnet 1, a gradient coil 2, a gradientmagnetic-field power source 3, a whole body (WB) coil 4, a receivingcoil device 5, a bed 6, a transmitting circuitry 7, a receivingcircuitry 8, a gantry 9, an interface 10, a display 11, a memorycircuitry 12, and processing circuitries 13, 14, 15, and 16. The MRIapparatus 100 does not include a subject S (e.g., a human body). The MRIapparatus 100 is an example of a medical information processingapparatus.

Specifically, the static magnet 1 is formed into substantially acylindrical shape (including the one that has an elliptical shape incross-section perpendicular to the center axis) with a hollow togenerate a static magnetic field in the imaging space formed on theinner circumference side. The static magnet 1 includes, for example, acooling container formed in substantially a cylindrical shape and amagnet, such as a superconducting magnet, immersed in a coolant (e.g.,liquid helium) filled in the cooling container. The static magnet 1 maygenerate a static magnetic field by using, for example, a permanentmagnet.

The gradient coil 2 generates a gradient magnetic field in the imagingspace where the subject S is placed. Specifically, the gradient coil 2is formed into substantially a cylindrical shape (including the one thathas an elliptical shape in cross-section perpendicular to the centeraxis) with a hollow and includes a plurality of gradient coils havingsubstantially a cylindrical shape and laminated in a radial direction.The gradient coils generate gradient magnetic fields along thedirections of the respective axes, i.e., the X-axis, the Y-axis, and theZ-axis that are orthogonal to each other, in the imaging space formed onthe inner circumference side based on the current supplied from thegradient magnetic-field power source 3.

More specifically, the gradient coil 2 includes an X coil that generatesa gradient magnetic field along the X-axis direction, a Y coil thatgenerates a gradient magnetic field along the Y-axis direction, and a Zcoil that generates a gradient magnetic field along the Z-axisdirection. The X-axis, the Y-axis, and the Z-axis constitute anapparatus coordinate system unique to the MRI apparatus 100. Forexample, the X-axis is set in a horizontal direction perpendicular tothe center axis of the gradient coil 2, and the Y-axis is set in avertical direction perpendicular to the center axis of the gradient coil2. Furthermore, the Z-axis is set along the center axis of the gradientcoil 2.

The gradient magnetic-field power source 3 individually supplies theelectric current to each of the X coil, the Y coil, and the Z coilincluded in the gradient coil 2 to generate gradient magnetic fields inthe imaging space along each axis direction, i.e., the X-axis, Y-axis,and the Z-axis directions. Specifically, the gradient magnetic-fieldpower source 3 supplies the electric current to the X coil, the Y coil,and the Z coil as appropriate to generate gradient magnetic fields alonga read-out direction, a phase encoding direction, and a slice directionthat are perpendicular to each other. The axis along the read-outdirection, the axis along the phase encoding direction, and the axisalong the slice direction constitute a logical coordinate system thatdefines a slice area or a volume area to be imaged.

In the example described below, the axis along the read-out direction,the axis along the phase encoding direction, and the axis along theslice direction, which constitute the logical coordinate system,correspond to the X-axis, the Y-axis, and the Z-axis, respectively,which constitute the apparatus coordinate system. However, thecorrespondence relationship between the logical coordinate system andthe apparatus coordinate system is not limited thereto and may bechanged as appropriate.

The gradient magnetic fields along the read-out direction, the phaseencoding direction, and the slice direction are superimposed on thestatic magnetic field generated by the static magnet 1 so as to give thespatial position information to magnetic resonance (MR) signalsgenerated from the subject S. Specifically, a gradient magnetic fieldGro in the read-out direction changes the frequency of an MR signal inaccordance with the position in the read-out direction to give theposition information along the read-out direction to the MR signal. Agradient magnetic field Gpe in the phase encoding direction changes thephase of an MR signal along the phase encoding direction to give theposition information along the phase encoding direction to the MRsignal. A gradient magnetic field Gss in the slice direction gives theposition information along the slice direction to the MR signal. Forexample, the gradient magnetic field Gss in the slice direction is usedto determine the direction, the thickness, or the number of pieces of aslice area if the imaging area is a slice area and is used to change thephase of an MR signal in accordance with the position in the slicedirection if the imaging area is a volume area.

The WB coil 4 is a radio frequency (RF) coil that is disposed inside thegradient coil 2 to function as a transmitting coil that applies an RFmagnetic field to the imaging space where the subject S is placed andfunctions as a receiving coil that receives an MR signal generated fromthe subject S due to the effect of the RF magnetic field. Specifically,the WB coil 4 is formed in substantially a cylindrical shape (includingthe one that has an elliptical shape in cross-section perpendicular tothe center axis of the cylinder) to apply an RF magnetic field to theimaging space formed in the cylinder based on a high-frequency pulsesignal supplied from the transmitting circuitry 7. The WB coil 4receives the MR signal generated from the subject S due to the effect ofthe RF magnetic field and outputs the received MR signal to thereceiving circuitry 8.

The receiving coil device 5 is an RF coil that receives an MR signalgenerated from the subject S. For example, the receiving coil device 5is prepared for each site of the subject S and is disposed near thetarget site to be captured when the subject S is captured. The receivingcoil device 5 includes one or more independent coil elements(hereinafter also simply referred to as “elements”) that receive MRsignals generated from the subject S due to the effect of the RFmagnetic field applied by the WB coil 4. The receiving coil device 5amplifies the MR signal received by the element and outputs the MRsignal to the receiving circuitry 8. The receiving coil device 5 mayfurther function as a transmitting coil that applies an RF magneticfield to the subject S. In this case, the receiving coil device 5 iscoupled to the transmitting circuitry 7 so as to apply an RF magneticfield to the subject S based on an RF pulse signal supplied from thetransmitting circuitry 7.

The bed 6 includes a top plate 6 a on which the subject S is placed sothat the top plate 6 a where the subject S is placed is moved in theimaging space when the subject S is captured. For example, the bed 6 isdisposed such that the longitudinal direction of the top plate 6 a isparallel to the center axis of the static magnet 1.

The transmitting circuitry 7 outputs, to the WB coil 4, the RF pulsesignal corresponding to the resonance frequency (Larmor frequency)unique to the target atomic nucleus placed in the static magnetic field.Specifically, the transmitting circuitry 7 includes a pulse generator,an RF generator, a modulator, and an amplifier. The pulse generatorgenerates the waveform of an RF pulse signal. The RF generator generatesan RF signal at the resonance frequency. The modulator modulates theamplitude of the RF signal generated by the RF generator with thewaveform generated by the pulse generator to generate an RF pulsesignal. The amplifier amplifies the RF pulse signal generated by themodulator and outputs the amplified RF pulse signal to the WB coil 4.

The receiving circuitry 8 generates MR signal data based on the MRsignal received by the WB coil 4 or the receiving coil device 5. Then,the receiving circuitry 8 outputs the generated MR signal data to theprocessing circuitry 14.

The gantry 9 includes a hollow bore 9 a formed in substantially acylindrical shape (including the one that has an elliptical shape incross-section perpendicular to the center axis) to support the staticmagnet 1, the gradient coil 2, and the WB coil 4. Specifically, thegantry 9 supports the static magnet 1, the gradient coil 2, and the WBcoil 4 in a state where the gradient coil 2 is disposed on the innercircumference side of the static magnet 1, the WB coil 4 is disposed onthe inner circumference side of the gradient coil 2, and the bore 9 a isdisposed on the inner circumference side of the WB coil 4. The spacewithin the bore 9 a included in the gantry 9 is the imaging space wherethe subject S is placed when the subject S is captured.

In the example described here, the MRI apparatus 100 has what is calleda tunnel configuration in which the static magnet 1, the gradient coil2, and the WB coil 4 are formed to have substantially a cylindricalshape; however, the embodiment is not limited thereto. For example, theMRI apparatus 100 may have what is called an opened configuration inwhich a pair of static magnets, a pair of gradient coil units, and apair of RF coils are disposed to face each other with the imaging spacewhere the subject S is placed interposed therebetween. In this case, thespace sandwiched between the pair of static magnets, the pair ofgradient coil units, and the pair of RF coils corresponds to a bore inthe tunnel structure.

The interface 10 receives input operations of various instructions andvarious kinds of information from the operator. Specifically, theinterface 10 is coupled to the processing circuitry 16 to convert aninput operation received from the operator into an electric signal andoutputs the electric signal to the processing circuitry 16. For example,the interface 10 is implemented by using a track ball for setting, forexample, an imaging condition or a region of interest (ROI), a switchbutton, a mouse, a keyboard, a touch pad for performing an inputoperation with the touch on an operating surface, a touch screen inwhich a display screen and a touch pad are integrated, a non-contactinput circuitry using an optical sensor, or a voice input circuitry. Inthis description, the interface 10 is not limited to the one including aphysical operating component such as a mouse or a keyboard. Examples ofthe interface 10 include an electric signal processing circuitry thatreceives an electric signal corresponding to the input operation from anexternal input device provided separately from the apparatus and outputsthe electric signal to a control circuitry.

The display 11 presents various kinds of information and images.Specifically, the display 11 is coupled to the processing circuitry 16to convert various types of information or image data transmitted fromthe processing circuitry 16 into an electric signal for display andoutput the electric signal. The display 11 is implemented by using, forexample, a liquid crystal monitor, a cathode ray tube (CRT) monitor, ora touch panel.

The memory circuitry 12 stores various types of data. Specifically, thememory circuitry 12 stores MR signal data and image data. The memorycircuitry 12 is implemented by using, for example, a semiconductormemory device such as a random access memory (RAM) or a flash memory, ahard disk, or an optical disk.

The processing circuitry 13 includes a bed control function 13 a. Thebed control function 13 a outputs a control electric signal to the bed 6so as to control the operation of the bed 6. For example, the bedcontrol function 13 a receives the operator's instruction for moving thetop plate 6 a in the longitudinal direction, the vertical direction, orthe lateral direction via the interface 10 and operates the movementmechanism of the top plate 6 a of the bed 6 so that the top plate 6 a ismoved in accordance with the received instruction.

The processing circuitry 14 includes an acquisition function 14 a. Theacquisition function 14 a executes various pulse sequences to acquire MRsignal data on the subject S. Specifically, the acquisition function 14a drives the gradient magnetic-field power source 3, the transmittingcircuitry 7, and the receiving circuitry 8 in accordance with thesequence execution data output from the processing circuitry 16 toexecute the pulse sequence. The sequence execution data is datarepresenting a pulse sequence and is information that defines the timingat which the gradient magnetic-field power source 3 supplies an electriccurrent to the gradient coil 2, the intensity of the supplied electriccurrent, the timing at which the transmitting circuitry 7 supplies an RFpulse signal to the WB coil 4, the intensity of the supplied RF pulsesignal, or the timing at which the receiving circuitry 8 detects an MRsignal. The acquisition function 14 a receives MR signal data from thereceiving circuitry 8 as a result of the pulse sequence execution andstores the received MR signal data in the memory circuitry 12. The setof MR signal data received by the acquisition function 14 a is arrangedin two dimensions or three dimensions in accordance with the positioninformation given by the read-out gradient magnetic field, the phaseencoding gradient magnetic field, and the slice gradient magnetic fielddescribed above so as to be stored as the data forming the k-space inthe memory circuitry 12.

The processing circuitry 15 includes a reconstruction function 15 a. Thereconstruction function 15 a generates image data based on the MR signaldata stored in the memory circuitry 12. Specifically, the reconstructionfunction 15 a reads MR signal data stored in the memory circuitry 12 byusing the acquisition function 14 a and performs post-processing, i.e.,reconstruction processing such as Fourier transform (FT), on the read MRsignal data to generate image data. The reconstruction function 15 astores the generated image data in the memory circuitry 12.

The processing circuitry 16 includes a primary control function 16 a, afirst calculation function 16 b, a second calculation function 16 c, anda denoising processing function 16 d. The primary control function 16 acontrols each component included in the MRI apparatus 100 to perform theoverall control of the MRI apparatus 100. Specifically, the primarycontrol function 16 a causes the display 11 to present a graphical userinterface (GUI) that receives an input operation of various types ofinstructions and information from the operator. The primary controlfunction 16 a controls each component included in the MRI apparatus 100in response to the input operation received via the interface 10. Forexample, the primary control function 16 a receives the input of animaging condition from the operator through the interface 10. Theprimary control function 16 a generates sequence execution data based onthe received imaging condition and transmits the sequence execution datato the processing circuitry 14 so as to execute various pulse sequences.For example, in response to a request from the operator, the primarycontrol function 16 a reads image data from the memory circuitry 12 andoutputs the image data to the display 11. The first calculation function16 b, the second calculation function 16 c, and the denoising processingfunction 16 d are described later.

The above-described processing circuitries 13, 14, 15, and 16 areimplemented by using for example a processor. In this case, for example,the processing function provided by each processing circuitry is storedin the memory circuitry 12 in the form of a program executable by acomputer. Each processing circuitry reads and executes each program fromthe memory circuitry 12 to perform the function corresponding to eachprogram. Each processing circuitry may be configured by using aplurality of processors so that each of the processors executes aprogram to perform each processing function. The processing functionprovided by each processing circuitry may be performed by beingseparated or combined in one or more processing circuitries asappropriate. The single memory circuitry 12 stores the programcorresponding to each processing function in this description; however,a configuration may be such that a plurality of memory circuitries isdistributed so that processing circuitry reads the corresponding programfrom an individual memory circuitry.

The configuration of the MRI apparatus 100 according to the firstembodiment has been described above. With the above-describedconfiguration, the MRI apparatus 100 performs the following processingfunction in order to estimate the denoising intensity with highaccuracy.

The MRI apparatus 100 according to the first embodiment enables thehigh-speed imaging using parallel imaging (PI). For example, the PI usesthe fact that the sensitivity is different depending on the arrangementof coils so that the k-space data is simultaneously captured anddecimated by a plurality of coils and an image (reconstruction image) isgenerated from the obtained k-space data while artifacts are suppressed.In the example described below, the PI is executed; however, embodimentsare not limited thereto.

With reference to FIG. 2 , the steps of a process performed by the MRIapparatus 100 according to the first embodiment are described. FIG. 2 isa flowchart illustrating the steps of a process performed by the MRIapparatus 100 according to the first embodiment. The steps of theprocess illustrated in FIG. 2 are started in response to, for example,an imaging start request input by the operator.

With reference to FIGS. 3 and 4 , FIG. 2 is described. FIGS. 3 and 4 arediagrams illustrating a processing function of the MRI apparatus 100according to the first embodiment.

As illustrated in FIG. 2 , the primary control function 16 a sets animaging condition (Step S101). For example, the primary control function16 a receives the input of an imaging condition from the operator viathe interface 10. The primary control function 16 a generates sequenceexecution data based on the received imaging condition and transmits thegenerated sequence execution data to the acquisition function 14 a.

Subsequently, the acquisition function 14 a executes the preparatoryscan (Step S102). For example, the acquisition function 14 a drives thegradient magnetic-field power source 3, the transmitting circuitry 7,and the receiving circuitry 8 in accordance with the sequence executiondata output from the primary control function 16 a to execute thepreparatory scan. Examples of the preparatory scan include the scan foracquiring an image for positioning, the shimming scan for correcting thenon-uniformity of a static magnetic field, or the scan (sensitivity mapscan) for acquiring a sensitivity map.

During the sensitivity map scan, the acquisition function 14 a acquires“noise data” and “coil sensitivity information”. For example, theacquisition function 14 a performs the noise scan that is the scanwithout applying an RF magnetic field on the WB coil 4 and each elementto acquire “noise data”. Typically, the noise data is used to calculatethe noise gain for correcting the deviation between the signal values ofchannels obtained during the noise scan and the noise matrix indicatingthe correlation between elements. The acquisition function 14 aindividually performs the scan on the WB coil 4 and each element. Theacquisition function 14 a compares the information (or image data)scanned by the WB coil 4 with the information (or image data) scanned byeach element to generate “coil sensitivity information” on each element.

In order to acquire only the noise data, it is preferable to perform thenoise scan without transmitting an RF pulse. However, an RF pulse may beapplied as long as a generated nuclear magnetic resonance (NMR) signal(MR signal) does not affect the estimation of the amount of noise. Forexample, an RF pulse having an extremely small flip angle may be appliedduring the noise scan.

In other words, the preparatory scan includes the scan that acquiresnoise data without transmitting an RF pulse having more than a certainintensity. The RF pulse having more than a certain intensity is an RFpulse such that a generated NMR signal affect the estimation of theamount of noise.

The first calculation function 16 b calculates the noise intensity andthe conversion factor for the preparatory scan (Step S103). For example,the first calculation function 16 b calculates the noise intensity fromthe noise data acquired during the preparatory scan.

With reference to FIG. 3 , the process to calculate the noise intensityis described. As illustrated in FIG. 3 , for example, the reconstructionfunction 15 a performs Fast Fourier Transform (FFT) on the acquired dataon each channel (each element), which is acquired during the noise scan,to generate noise data that is data in the real space. The firstcalculation function 16 b calculates the complex average value and thestandard deviation of each pixel value in the noise data on all theslices and all the channels through the complex arithmetic. The firstcalculation function 16 b outputs the thus calculated standard deviationas a noise intensity “NoiseSD_map”. That is, the first calculationfunction 16 b calculates the noise intensity based on data obtained bytransforming the k-space data acquired during the preparatory scan intothe real-space data.

The first calculation function 16 b calculates a conversion factor forthe preparatory scan based on the imaging condition for the preparatoryscan. The conversion factor is a factor for adjusting the differencebetween the imaging condition for the preparatory scan and the imagingcondition for the main scan. The conversion factor for the preparatoryscan (for the sensitivity map scan) is an example of a first conversionfactor.

For example, the first calculation function 16 b uses the followingEquation (1) to calculate the conversion factor for the preparatoryscan. In Equation (1), Rg represents a signal amplification gain in thereceiving circuitry 8. Nex represents the number of averages in thek-space. Nx represents the matrix size in the frequency encodingdirection. Ny represents the matrix size in the phase encodingdirection. Nz represents the number of slice encoding for 3DFT. BWrepresents the bandwidth per pixel (BW=Bandwidth/Nx). Further, g is thefactor indicating an amplification gain of the noise component by theunfolding process during parallel imaging. A represents the accelerationfactor of high-speed imaging using compressed sensing (CS).

${{CONVERSION}{FACTOR}} = {g*A*\frac{{Rg}*{Nx}*\sqrt{{BW}*{Ny}*{Nz}}}{\sqrt{Nex}}}$

The parameters Rg, Nex, Nx, Ny, Nz, BW, g, and A included in Equation(1) may be acquired from the imaging condition. That is, the firstcalculation function 16 b acquires the parameters Rg, Nex, Nx, Ny, Nz,BW, g, and A from the imaging condition for the preparatory scan. Then,the first calculation function 16 b applies each of the acquiredparameters to Equation (1) to calculate a conversion factor “C map” forthe preparatory scan.

As described above, the first calculation function 16 b calculates thenoise intensity “NoiseSD_map” and the conversion factor “C_map” for thepreparatory scan. FIG. 3 and Equation (1) are merely examples, andembodiments are not limited thereto. For example, the conversion factormay be multiplied by any coefficient. Equation (1) described above isnot exclusively applied to 3DFT or CS. For example, in the case of 2DFT,Nz is “1”. Furthermore, in the case where CS is not applied, A is “1”.

The acquisition function 14 a executes the main scan (Step S104). Forexample, the acquisition function 14 a drives the gradientmagnetic-field power source 3, the transmitting circuitry 7, and thereceiving circuitry 8 in accordance with the sequence execution dataoutput from the primary control function 16 a to execute the main scan.The main scan is, for instance, scan for generating a diagnostic image.

The reconstruction function 15 a generates a reconstruction image (StepS105). For example, the reconstruction function 15 a uses thesensitivity map to generate an unfolded image (reconstruction image)from MR signals acquired during the main scan. The reconstructionfunction 15 a stores the reconstructed image data in the memorycircuitry 12. The thus generated reconstruction image is image databefore a denoising process.

The first calculation function 16 b calculates the conversion factor forthe main scan (Step S106). For example, the first calculation function16 b calculates the conversion factor for the main scan based on theimaging condition for the main scan. The conversion factor for the mainscan is an example of a second conversion factor.

For example, the first calculation function 16 b acquires the parametersRg, Nex, Nx, Ny, Nz, BW, g, and A from the imaging condition for themain scan. The first calculation function 16 b applies the acquiredparameters to Equation (1) to calculate a conversion factor “C” for themain scan.

The second calculation function 16 c calculates the denoising intensitybased on the noise intensity, the conversion factor for the preparatoryscan, and the conversion factor for the main scan (Step S107). Thedenoising processing function 16 d executes a denoising process on areconstruction image based on the denoising intensity (Step S108).

With reference to FIG. 4 , the denoising intensity calculation processand the denoising process are described. For example, the secondcalculation function 16 c acquires the noise intensity “NoiseSD_map”,the conversion factor “C_map” for the preparatory scan, and theconversion factor “C” for the main scan, calculated by the firstcalculation function 16 b. The second calculation function 16 c appliesthe acquired parameters to the equation illustrated in FIG. 4 tocalculate a denoising intensity “NoiseSD”. In the equation(NoiseSD=NoiseSD_map*C/C_map*α) illustrated in FIG. 4 , α is anadjustment factor.

In other words, the second calculation function 16 c calculates thedenoising intensity based on the noise intensity, the first conversionfactor corresponding to the imaging condition for the preparatory scan,and the second conversion factor corresponding to the imaging conditionfor the main scan. Specifically, the second calculation function 16 ccalculates the denoising intensity based on the value obtained bymultiplying the noise intensity by the ratio of the second conversionfactor to the first conversion factor.

The denoising processing function 16 d uses the reconstruction imageacquired during the main scan as a filter input image and executes thedenoising process using the shrinkage method that uses the denoisingintensity “NoiseSD”. For the denoising process using the shrinkagemethod, any known technique may be selected and applied. For example,the denoising processing function 16 d uses the denoising intensity todetermine the threshold for the denoising process using the shrinkagemethod. The denoising processing function 16 d uses the determinedthreshold to perform the denoising process. Thus, the denoisingprocessing function 16 d generates the denoised image that is obtainedafter noise is removed from the reconstruction image.

As described above, the second calculation function 16 c calculates thedenoising intensity used for the denoising process based on the noiseintensity and the difference between the imaging condition for thepreparatory scan and the imaging condition for the main scan, thedenoising process being applied to data obtained by the main scan. Thedenoising processing function 16 d performs the denoising process on thereconstruction image acquired during the main scan based on thedenoising intensity calculated by the second calculation function 16 c.

The primary control function 16 a causes the denoised image to bedisplayed (Step S109). For example, the primary control function 16 acauses the display 11 to present the denoised image stored in the memorycircuitry 12. To display the denoised image, the primary controlfunction 16 a may use a known image processing technique such as arendering process as appropriate.

The steps of the process described in FIG. 2 are merely an example, andthe details illustrated in FIG. 2 are not a limitation. For example, theMRI apparatus 100 may shuffle and execute the steps of the process asappropriate as long as the consistency is ensured for the details of theprocess. For example, the calculation operation at Step S103 is notnecessarily performed immediately after the operation at Step S102 aslong as the calculation operation at Step S103 is completed before theoperation at Step S107. For example, the calculation operation at StepS103 may be executed simultaneously with the calculation operation atStep S106. For example, the reconstruction operation at Step S105 is notnecessarily performed immediately after the operation at Step S104 aslong as the reconstruction operation at Step S105 is completed beforethe operation at Step S108.

As described above, in the MRI apparatus 100 according to the firstembodiment, the first calculation function 16 b calculates the noiseintensity from the noise data acquired during the preparatory scan. Thesecond calculation function 16 c calculates the denoising intensity usedfor the denoising process from the noise intensity based on thedifference between the imaging condition for the preparatory scan andthe imaging condition for the main scan. Thus, the MRI apparatus 100 mayestimate the denoising intensity with high accuracy. As a result, theMRI apparatus 100 may generate a high-quality reconstruction image fromwhich noise has been removed with high accuracy.

The MRI apparatus 100 may execute the above-described denoisingintensity calculation process without adding a special scan. Thus, theMRI apparatus 100 may accurately estimate the denoising intensity whileminimizing the extension of an examination time.

Modified Example 1 of the First Embodiment

Although the PI is executed in the example described in the firstembodiment, embodiments are not limited thereto. For example, eventhough the PI is not executed, the MRI apparatus 100 may perform anadditional noise scan to perform the above-described denoising intensitycalculation process. For example, when the PI is not executed, the MRIapparatus 100 performs the above-described process by using Equation (1)in which “g” (the factor indicating an amplification gain of the noisecomponent by the unfolding process during parallel imaging) is “1”.

Modified Example 2 of the First Embodiment

Although the denoising intensity of the main scan is calculated based onthe noise intensity and a difference between an imaging condition forthe preparatory scan and an imaging condition for a main scan in theexample described in the first embodiment, embodiments are not limitedthereto. For example, the scan does not need to be “preparatory scan” ifit is the scan that can calculate the noise intensity. In this case, thedenoising intensity is calculated based on the noise intensity and thedifference between an imaging condition for a main scan “A” to becalculated the noise intensity and an imaging condition for a main scan“B” performing the denoising process.

In addition, the main scan “A” may be described as “a first scan”. Dataacquired during the first scan may be described as “first data”. Themain scan “B” may be described as “a second scan”. Data acquired duringthe second scan may be described as “second data”.

Modified Example 3 of the First Embodiment

Although the preparatory scan is carried out before the main scan in theexample described in the first embodiment, embodiments are not limitedthereto. For example, the scan (corresponding to preparatory scan) tocalculate the noise intensity may be carried out after the main scan. Inother words, the scan to calculate the noise intensity may be a scan tobe carried out independently by the main scan.

Second Embodiment

In the example described in the first embodiment, the conversion valueof the noise intensity of noise data is used as a denoising intensity;however, embodiments are not limited thereto. The MRI apparatus 100according to the second embodiment may estimate the denoising intensitybased on the pixel value in the background area of a reconstructionimage acquired during the main scan.

Although the MRI apparatus 100 according to the second embodiment hasthe same configuration as that of the MRI apparatus 100 illustrated inFIG. 1 , the MRI apparatuses 100 are different in part of the process bythe second calculation function 16 c and part of the process by thedenoising processing function 16 d. In the second embodiment, adifference from the first embodiment is described.

FIG. 5 is a diagram illustrating a processing function of the MRIapparatus 100 according to the second embodiment. As illustrated in FIG.5 , the second calculation function 16 c acquires the noise intensity“NoiseSD_map” calculated by the first calculation function 16 b, theconversion factor “C_map” for the preparatory scan, and the conversionfactor “C” for the main scan. The second calculation function 16 capplies the acquired parameters to the equation(NoiseSDtmp=NoiseSD_map*C/C_map) illustrated in FIG. 5 to calculate thetemporary denoising intensity “NoiseSDtmp” (S11).

The temporary denoising intensity corresponds to the value obtained bycalculating the “denoising intensity (NoiseSD)” described in the firstembodiment with the adjustment factor (α) of “1”. That is, the noiseintensity “NoiseSD_map” used for calculating the temporary denoisingintensity is a value calculated during the process of the firstcalculation function 16 b according to the first embodiment (see FIG. 3). The “temporary denoising intensity” may be the value obtained bymultiplication using a number other than “1” as the adjustment factor.Thus, the temporary denoising intensity is substantially the sameparameter as the denoising intensity described in the first embodimentexcept that the temporary denoising intensity is not directly usedduring the denoising process.

The second calculation function 16 c sets a threshold based on thetemporary denoising intensity (S12). The threshold corresponds to therange of pixel values for specifying the background area in thereconstruction image. For example, the second calculation function 16 csets “0.0” as the lower limit of the threshold. The second calculationfunction 16 c sets “P*NoiseSDtmp” as the upper limit of the threshold.The value of P is determined in consideration of a noise distribution.For example, in the case of a normal distribution, “3” is selected asthe value of P so that 95% of the distribution is included.

The second calculation function 16 c extracts, from filter input image(reconstruction image), a pixel of which the magnitude of the signalintensity (pixel value) is within the range of the threshold (S13). Theextracted pixel substantially corresponds to the background area of thereconstruction image.

The second calculation function 16 c calculates the standard deviationof the pixel values of the extracted pixels through the complexarithmetic and multiplies the calculated standard deviation by theadjustment factor (α) to calculate the denoising intensity “NoiseSD”(S14).

The denoising processing function 16 d executes the denoising processusing the shrinkage method with the denoising intensity “NoiseSD” on afilter input image (S15). Any known technique may be selected andapplied to the denoising process using the shrinkage method. Thus, thedenoising processing function 16 d generates a denoised image obtainedafter noise has been removed from the reconstruction image.

As described above, in the MRI apparatus 100 according to the secondembodiment, the second calculation function 16 c determines the range ofthe signal value of the background area by using the denoising intensityand calculates the standard deviation of the pixel values of thebackground area in the reconstruction image. The denoising processingfunction 16 d uses the calculated standard deviation to perform thedenoising process. Thus, the MRI apparatus 100 may estimate thedenoising intensity based on the pixel value of the background area inthe reconstruction image acquired during the main scan.

That is, the second calculation function 16 c specifies the backgroundarea of the reconstruction image by using the denoising intensity(temporary denoising intensity) and calculates the standard deviation ofthe pixel values of the pixels included in the specified backgroundarea. The denoising processing function 16 d performs the denoisingprocess using the calculated standard deviation.

For the MRI, originally, it is preferable that the denoising intensityis estimated from the “background area” in which the NMR signal is notincluded. Therefore, the MRI apparatus 100 according to the secondembodiment does not directly use the “denoising intensity (NoiseSD)”described in the first embodiment but estimates the background area ofthe reconstruction image by using the “denoising intensity (NoiseSD)” asthe “temporary denoising intensity (NoiseSDtmp)”. The MRI apparatus 100according to the second embodiment calculates the proper denoisingintensity “NoiseSD” based on the pixel values of the pixels included inthe estimated background area of the reconstruction image. Accordingly,the MRI apparatus 100 according to the second embodiment may calculatethe denoising intensity more appropriately.

The description of FIG. 5 is merely an example, and embodiments are notlimited thereto. For example, when the CS is applied, the secondcalculation function 16 c may set the upper limit of the threshold inconsideration of a regularization factor.

Other Embodiments

In addition to the embodiments described above, various differentembodiments may be implemented.

Other Parameters indicating the Noise Intensity

In the example described according to the above embodiment, the standarddeviation is used as the noise intensity; however, embodiments are notlimited thereto. The reason why the standard deviation is used in theabove embodiment is that the noise distribution in an MR image(real-space image) conforms with a Gaussian distribution. For example,when the denoising process is performed in another space instead of thereal space, the noise distribution may have a distribution that does notconform with a Gaussian distribution. In such a case, a differentparameter (e.g., an average value or a statistical value) other than thestandard deviation may be used as the noise intensity depending on thedistribution.

Parameter of the Conversion Factor

The parameters used to calculate the conversion factor are not limitedto Rg, Nex, Nx, Ny, Nz, BW, g and A described in Equation (1). Forexample, when zero padding or zero filling is performed, the number ofdatasets to be filled with zero may be used as a parameter used tocalculate the conversion factor. Zero filling is allocating the value“0” completely including no noise to the k-space. Therefore, thezero-filled k-space data seems to have a reduced amount of noise inaccordance with the number of datasets filled with zero. For thisreason, when zero filling is performed, it is preferable to adjust theconversion factor so as to be decreased in accordance with the number ofdatasets filled with zero.

In other words, the first calculation function 16 b calculates the firstconversion factor based on at least one of the following: the signalamplification gain in the receiving circuitry included in the imagingcondition for the preparatory scan, the number of averages in thek-space, the matrix size in the frequency encoding direction, the matrixsize in the phase encoding direction, the number of slice encoding, thebandwidth per pixel, the factor indicating the unfolding performanceduring parallel imaging, the acceleration factor of the high-speedimaging using the compressed sensing, and the number of datasets filledwith zero.

Furthermore, the first calculation function 16 b calculates the secondconversion factor based on at least one of the following: the signalamplification gain in the receiving circuitry included in the imagingcondition for the main scan, the number of averages in the k-space, thematrix size in the frequency encoding direction, the matrix size in thephase encoding direction, the number of slice encoding, the bandwidthper pixel, the factor indicating the unfolding performance duringparallel imaging, the acceleration factor of the high-speed imagingusing the compressed sensing, and the number of datasets filled withzero.

Medical Information Processing Apparatus

In the example described according to the above embodiment, the MRIapparatus 100 is applied as an example of the medical informationprocessing apparatus; however, embodiments are not limited thereto. Forexample, an information processing apparatus such as a personal computeror a workstation may be used as the medical information processingapparatus.

In this case, processing circuitry of the medical information processingapparatus performs the processing functions that are similar to thefirst calculation function 16 b, the second calculation function 16 c,and the denoising processing function 16 d. The medical informationprocessing apparatus receives information such as the noise data, theimaging condition for the preparatory scan, and the imaging conditionfor the main scan from the MRI apparatus to execute each of theprocessing functions so as to calculate the denoising intensity.

The components of each device illustrated are conceptual in terms offunctionality and do not necessarily need to be physically configured asillustrated in the drawings. Specifically, the specific forms ofseparation and combination of each device are not limited to thosedepicted in the drawings, and a configuration may be such that all orsome of the devices are functionally or physically separated or combinedin any unit depending on various types of loads or usage. All or any ofvarious processing functions performed by each device may be implementedby a CPU and a program analyzed and executed by the CPU or may beimplemented as wired logic hardware.

Among the processes described in the above embodiments, all or part ofthe processes that are automatically performed as described above may beperformed manually. Furthermore, all or part of the processes that aremanually performed as described above may be performed automatically byusing a known method. Furthermore, the process steps, the control steps,the specific names, and the information including various types of dataand parameters as described in the above description and the drawingsmay be optionally changed except as otherwise noted.

The medical information processing method described in the aboveembodiments may be implemented when a prepared medical informationprocessing program is executed by a computer such as a personal computeror a workstation. The medical information processing program may bedistributed via a network such as the Internet. The medical informationprocessing method may be recorded in a computer-readable recordingmedium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, or aDVD and may be read from the recording medium by the computer so as tobe executed.

According to at least one of the embodiments described above, it ispossible to estimate the denoising intensity with high accuracy.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A medical information processing apparatuscomprising processing circuitry configured to: calculate a noiseintensity from data acquired during a first MR (Magnetic Resonance) scanfor obtaining an MR signal; and calculate a denoising intensity used fora denoising process based on the noise intensity and a differencebetween an imaging condition for the first MR scan and an imagingcondition for a second MR scan, the denoising process being applied todata obtained by the second MR scan, wherein the processing circuitry isfurther configured to calculate the denoising intensity based on thenoise intensity, a first conversion factor corresponding to the imagingcondition for the first MR scan, and a second conversion factorcorresponding to the imaging condition for the second MR scan.
 2. Themedical information processing apparatus according to claim 1, whereinthe processing circuitry is further configured to calculate thedenoising intensity based on a value obtained by multiplying the noiseintensity by a ratio of the second conversion factor to the firstconversion factor.
 3. The medical information processing apparatusaccording to claim 1, wherein the processing circuitry is furtherconfigured to calculate the first conversion factor based on at leastone of the following: a signal amplification gain in a receivingcircuitry included in the imaging condition for the first MR scan, anumber of averages in a k-space, a matrix size in a frequency encodingdirection, a matrix size in a phase encoding direction, a number ofslice encoding, a bandwidth per pixel, a factor indicating an unfoldingperformance during parallel imaging, an acceleration factor ofhigh-speed imaging using compressed sensing, and a number of datasetsfilled with zero.
 4. The medical information processing apparatusaccording to claim 1, wherein the processing circuitry is furtherconfigured to calculate the second conversion factor based on thefollowing: a signal amplification gain in a receiving circuitry includedin the imaging condition for the second MR scan, a number of averages ina k-space, a matrix size in a frequency encoding direction, a matrixsize in a phase encoding direction, a number of slice encoding, and abandwidth per pixel.
 5. The medical information processing apparatusaccording to claim 1, wherein the processing circuitry is furtherconfigured to calculate the second conversion factor based on a factorindicating an amplification gain of a noise component by an unfoldingprocess during parallel imaging included in the imaging condition forthe second MR scan.
 6. The medical information processing apparatusaccording to claim 1, wherein the processing circuitry is furtherconfigured to calculate the second conversion factor based on anacceleration factor of high-speed imaging using compressed sensingincluded in the imaging condition for the second MR scan.
 7. The medicalinformation processing apparatus according to claim 1, wherein theprocessing circuitry further performs the denoising process on seconddata acquired during the second MR scan based on the denoisingintensity.
 8. The medical information processing apparatus according toclaim 5, wherein the processing circuitry is further configured to usethe denoising intensity to determine a threshold for a denoising processusing a shrinkage method, and use the threshold determined to performthe denoising process.
 9. The medical information processing apparatusaccording to claim 5, wherein the processing circuitry is furtherconfigured to specify a background area in the second data using thedenoising intensity, calculate a standard deviation of pixel values ofpixels included in the background area specified, and perform thedenoising process using the standard deviation calculated.
 10. Themedical information processing apparatus according to claim 1, whereinthe first MR scan includes a scan for acquiring the first data withouttransmitting a radio frequency (RF) pulse having more than certainintensity.
 11. The medical information processing apparatus according toclaim 10, wherein the RF pulse having less than the certain intensity isan RF pulse such that a generated nuclear magnetic resonance (NMR)signal does not affect estimation of an amount of noise.
 12. The medicalinformation processing apparatus according to claim 1, wherein theprocessing circuitry is further configured to calculate the noiseintensity based on data obtained by transforming k-space data acquiredduring the first MR scan into real-space data.
 13. The medicalinformation processing apparatus according to claim 1, wherein themedical information processing apparatus is a magnetic resonance imagingapparatus.
 14. The medical information processing apparatus according toclaim 1, wherein the second MR scan is main scan for generating adiagnostic image, and the first MR scan is a scan carried outindependently by the main scan.
 15. A medical information processingmethod comprising: receiving first data resulting from a first MR(Magnetic Resonance) scan for obtaining an MR signal; calculating anoise intensity from said first data acquired during the first MR scan;calculating a denoising intensity used for a denoising process based onthe noise intensity and a difference between an imaging condition forthe first MR scan and an imaging condition for a second MR scan;receiving second data resulting from the second MR scan; and applying adenoising process to the second data obtained by the second MR scan,wherein the calculating calculates the denoising intensity based on thenoise intensity, a first conversion factor corresponding to the imagingcondition for the first MR scan, and a second conversion factorcorresponding to the imaging condition for the second MR scan.
 16. Amedical information processing apparatus comprising processing circuitryconfigured to: calculate a noise intensity from data acquired during afirst MR (Magnetic Resonance) scan for obtaining an MR signal; andcalculate a denoising intensity used for a denoising process based onthe noise intensity and a difference between an imaging condition forthe first MR scan and an imaging condition for a second MR scan, thedenoising process being applied to data obtained by the second MR scan,wherein the first MR scan includes a scan for acquiring the first datawithout transmitting a radio frequency (RF) pulse having more thancertain intensity.
 17. A medical information processing apparatuscomprising processing circuitry configured to: calculate a noiseintensity from data acquired during a first MR (Magnetic Resonance) scanfor obtaining an MR signal; and calculate a denoising intensity used fora denoising process based on the noise intensity and a differencebetween an imaging condition for the first MR scan and an imagingcondition for a second MR scan, the denoising process being applied todata obtained by the second MR scan, wherein the processing circuitry isfurther configured to calculate the noise intensity based on dataobtained by transforming k-space data acquired during the first MR scaninto real-space data.
 18. A medical information processing methodcomprising: receiving first data resulting from a first MR (MagneticResonance) scan for obtaining an MR signal; calculating a noiseintensity from said first data acquired during the first MR scan;calculating a denoising intensity used for a denoising process based onthe noise intensity and a difference between an imaging condition forthe first MR scan and an imaging condition for a second MR scan;receiving second data resulting from the second MR scan; and applying adenoising process to the second data obtained by the second MR scan,wherein the first MR scan includes a scan for acquiring the first datawithout transmitting a radio frequency (RF) pulse having more thancertain intensity.
 19. A medical information processing methodcomprising: receiving first data resulting from a first MR (MagneticResonance) scan for obtaining an MR signal; calculating a noiseintensity from said first data acquired during the first MR scan;calculating a denoising intensity used for a denoising process based onthe noise intensity and a difference between an imaging condition forthe first MR scan and an imaging condition for a second MR scan;receiving second data resulting from the second MR scan; and applying adenoising process to the second data obtained by the second MR scan,wherein the calculating calculates the noise intensity based on dataobtained by transforming k-space data acquired during the first MR scaninto real-space data.